Hereinafter, a conventional synthesizer is described with reference to FIG. 31. The synthesizer carries out temperature compensation of a reference oscillator for outputting a reference oscillation signal.
FIG. 31 is a block diagram showing conventional synthesizer 100. In FIG. 31, conventional synthesizer 100 includes first frequency divider 102 for frequency-dividing a reference oscillation signal output from reference oscillator 101, comparator 103 for receiving an output signal from first frequency divider 102, and low-pass filter 104 for receiving an output signal from comparator 103 and outputting a signal voltage value having a near-DC frequency. Synthesizer 100 further includes oscillator 105 for outputting an oscillation signal based on the signal voltage value output from low-pass filter 104, which is input into second frequency divider 106 at the other side. As oscillator 105, a voltage controlled oscillator (VCO) is often used. Furthermore, synthesizer 100 includes second frequency divider 106 for frequency-dividing an output signal from oscillator 105 by a frequency division number designated by control circuit 107 according to channel designation. Comparator 103 compares an output signal from second frequency divider 106 with the output signal from first frequency divider 102.
The above-mentioned configuration is that of a general synthesizer. Synthesizer 100 shown in FIG. 31 further includes temperature sensor 108 for sensing an ambient temperature, and control circuit 107 for controlling a frequency division number of second frequency divider 106 based on a temperature sensed by temperature sensor 108. Thus, synthesizer 100 corrects shift of an oscillation frequency caused by the change of the ambient temperature by using temperature sensor 108. An example of the literature information of the related art of the invention of the present application includes Patent Document 1.
In conventional synthesizer 100, however, for example, a frequency adjustment unit of control circuit 107 is larger than predetermined value F, the phase noise of an oscillation signal is increased, and C/N of a reception device is deteriorated. Thus, excellent reception characteristics cannot be achieved.                [Patent Document 1] Japanese Patent Unexamined Publication No. H3-209917        